As shown in FIG. 8, an element, customarily called an arm, is indicated as 3, and is used for operating a jack (for example a scissor jack). At one end of the arm 3 is formed an arm hook 31, which hooks to the hook eye 511 of a screw head 51 of a jack 5, while the other end of the arm 3 is formed into a rectangular structure normally referred to as the rectangular joint. When a jack is to be operated, the arm hook 31 of the arm 3 is hooked up with the hook eye 511 on the screw head 51 and a handle bar 4 is secured on the rectangular joint through a hole formed in the middle of the handle bar. When the handle bar 4 is turned either clockwise or counterclockwise, the arm 3 and the screw of the jack 5 both turn accordingly so as to lift the jack 5 or restore it to its lowered position. Although the structure of the arm 3 meets the needs of operation of the jack 5, the length of the arm 3 is so limited that the operator has to adopt a squatting position to operate the device. As a result, operation efficiency is poor and thus it is easy for the operator to become fatigued. On the other hand, if the arm 3 is made longer to enable the operator to stand while operating, a new problem is created in that the arm 3 will be too long for easy storage. Particularly, the arm 3 and the rest of the jack is a tool set used in conjunction with and carried in an automobile. Thus convenient storage is an important factor that cannot be neglected.